Volume I Part 3 (1/2)

[Ill.u.s.tration: FIG. 11.--Rudimentary, or vestigial and useless, muscles of the human ear. (From _Gray's Anatomy_.)]

(2) _Panniculus carnosis._--A large number of the mammalia are able to move their skin by means of sub-cutaneous muscle--as we see, for instance, in a horse, when thus protecting himself against the sucking of flies. We, in common with the Quadrumana, possess an active remnant of such a muscle in the skin of the forehead, whereby we draw up the eyebrows; but we are no longer able to use other considerable remnants of it, in the scalp and elsewhere,--or, more correctly, it is rarely that we meet with persons who can. But most of the Quadrumana (including the anthropoids) are still able to do so. There are also many other vestigial muscles, which occur only in a small percentage of human beings, but which, when they do occur, present unmistakeable h.o.m.ologies with normal muscles in some of the Quadrumana and still lower animals[5].

[5] See especially Mr. John Wood's papers, _Proc. R. S._, xiii to xvi, and xviii; also _Journ. Anat._, i and iii. In this connexion Darwin refers to M. Richard, _Annls. d. Sc. Nat. Zoolg._, tom.

xviii, p. 13, 1852.

(3) _Feet._--It is observable that in the infant the feet have a strong deflection inwards, so that the soles in considerable measure face one another. This peculiarity, which is even more marked in the embryo than in the infant (see p. 153), and which becomes gradually less and less conspicuous even before the child begins to walk, appears to me a highly suggestive peculiarity. For it plainly refers to the condition of things in the Quadrumana, seeing that in all these animals the feet are similarly curved inwards, to facilitate the grasping of branches. And even when walking on the ground apes and monkeys employ to a great extent the outside edges of their feet, as does also a child when learning to walk. The feet of a young child are also extraordinarily mobile in all directions, as are those of apes. In order to show these points, I here introduce comparative drawings of a young ape and the portrait of a young male child. These drawings, moreover, serve at the same time to ill.u.s.trate two other vestigial characters, which have often been previously noticed with regard to the infant's foot. I allude to the incurved form of the legs, and the lateral extension of the great toe, whereby it approaches the thumb-like character of this organ in the Quadrumana. As in the case of the incurved position of the legs and feet, so in this case of the lateral extensibility of the great toe, the peculiarity is even more marked in embryonic than in infant life. For, as Prof. Wyman has remarked with regard to the foetus when about an inch in length, ”The great toe is shorter than the others; and, instead of being parallel to them, is projected at an angle from the side of the foot, thus corresponding with the permanent condition of this part in the Quadrumana[6].” So that this organ, which, according to Owen, ”is perhaps the most characteristic peculiarity in the human structure,”

when traced back to the early stages of its development, is found to present a notably less degree of peculiarity.

[6] _Proc. Nat. Hist. Soc._, Boston, 1863.

[Ill.u.s.tration: FIG. 12.--Portrait of a young male gorilla (after Hartmann).]

[Ill.u.s.tration: FIG. 13.--Portrait of a young male child.

Photographed from life, when the mobile feet were for a short time at rest in a position of extreme inflection.]

(4) _Hands._--Dr. Louis Robinson has recently observed that the grasping power of the whole human hand is so surprisingly great at birth, and during the first few weeks of infancy, as to be far in excess of present requirements on the part of a young child. Hence he concludes that it refers us to our quadrumanous ancestry--the young of anthropoid apes being endowed with similar powers of grasping, in order to hold on to the hair of the mother when she is using her arms for the purposes of locomotion. This inference appears to me justifiable, inasmuch as no other explanation can be given of the comparatively inordinate muscular force of an infant's grip. For experiments showed that very young babies are able to support their own weight, by holding on to a horizontal bar, for a period varying from one half to more than two minutes[7]. With his kind permission I here reproduce one of Dr. Robinson's instantaneous, and hitherto unpublished, photographs of a very young infant. This photograph was taken after the above paragraph (3) was written, and I introduce it here because it serves to show incidentally--and perhaps even better than the preceding figure--the points there mentioned with regard to the feet and great toes. Again, as Dr. Robinson observes, the att.i.tude, and the disproportionately large development of the arms as compared with the legs, give all the photographs a striking resemblance to a picture of the chimpanzee ”Sally” at the Zoological Gardens. For ”invariably the thighs are bent nearly at right angles to the body, and in no case did the lower limbs hang down and take the att.i.tude of the erect position.” He adds, ”In many cases no sign of distress is evinced, and no cry uttered, until the grasp begins to give way.”

[7] _Nineteenth Century_, November, 1891.

[Ill.u.s.tration: FIG. 14.--An infant, three weeks old, supporting its own weight for over two minutes. The att.i.tude of the lower limbs, feet, and toes, is strikingly simian. Reproduced from an instantaneous photograph, kindly given for the purpose by Dr. L.

Robinson.]

(5) _Tail._--The absence of a tail in man is popularly supposed to const.i.tute a difficulty against the doctrine of his quadrumanous descent. As a matter of fact, however, the absence of an external tail in man is precisely what this doctrine would expect, seeing that the nearest allies of man in the quadrumanous series are likewise dest.i.tute of an external tail. Far, then, from this deficiency in man const.i.tuting any difficulty to be accounted for, if the case were not so--i. e. if man _did_ possess an external tail,--the difficulty would be to understand how he had managed to retain an organ which had been renounced by his most recent ancestors. Nevertheless, as the anthropoid apes continue to present the rudimentary vestiges of a tail in a few caudal vertebrae below the integuments, we might well expect to find a similar state of matters in the case of man. And this is just what we do find, as a glance at these two comparative ill.u.s.trations will show.

(Fig. 15.) Moreover, during embryonic life, both of the anthropoid apes and of man, the tail much more closely resembles that of the lower kinds of quadrumanous animals from which these higher representatives of the group have descended. For at a certain stage of embryonic life the tail, both of apes and of human beings, is actually longer than the legs (see Fig. 16). And at this stage of development, also, the tail admits of being moved by muscles which later on dwindle away. Occasionally, however, these muscles persist, and are then described by anatomists as abnormalities. The following ill.u.s.trations serve to show the muscles in question, when thus found in adult man.

[Ill.u.s.tration: FIG. 15.--Sacrum of Gorilla compared with that of Man, showing the rudimentary tail-bones of each. Drawn from nature (_R. Coll. Surg. Mus._).]

[Ill.u.s.tration: FIG. 16.--Diagrammatic outline of the human embryo when about seven weeks old, showing the relations of the limbs and tail to the trunk (after Allen Thomson), _r_, the radial, and _u_, the ulnar, border of the hand and fore-arm; _t_, the tibial, and _f_, the fibular, border of the foot and lower leg; _au_, ear; _s_, spinal cord; _v_, umbilical cord; _b_, branchial gill-slits; _c_, tail.]

[Ill.u.s.tration: FIG. 17.--Front and back view of adult human sacrum, showing abnormal persistence of vestigial tail-muscles. (The first drawing is copied from Prof. Watson's paper in _Journl. Anat. and Physiol._, vol. 79: the second is compiled from different specimens.)]

(6) _Vermiform Appendix of the Caec.u.m._--This is of large size and functional use in the process of digestion among many herbivorous animals; while in man it is not only too small to serve any such purpose, but is even a source of danger to life--many persons dying every year from inflammation set up by the lodgement in this blind tube of fruit-stones, &c.

In the orang it is longer than in man (Fig. 18), as it is also in the human foetus proportionally compared with the adult. (Fig. 19.) In some of the lower herbivorous animals it is longer than the entire body.

Like vestigial structures in general, however, this one is highly variable. Thus the above cut (Fig. 19) serves to show that it may sometimes be almost as short in the orang as it normally is in man--both the human subjects of this ill.u.s.tration having been normal.

[Ill.u.s.tration: FIG. 18.--_Appendix vermiformis_ in Orang and in Man.

Drawn from dried inflated specimens in the Cambridge Museum by Mr.

J. J. Lister. _Il_, ilium; _Co_, colon; _C_, caec.u.m; W, a window cut in the wall of the caec.u.m; X X X, the appendix.]

[Ill.u.s.tration: FIG. 19.--The same, showing variation in the Orang.

Drawn from a specimen in the Museum of the Royal College of Surgeons.]

(7) _Ear._--Mr. Darwin writes:--

The celebrated sculptor, Mr. Woolner, informs me of one little peculiarity in the external ear, which he has often observed both in men and women.... The peculiarity consists in a little blunt point, projecting from the inwardly folded margin, or helix. When present, it is developed at birth, and, according to Prof. Ludwig Meyer, more frequently in man than in woman. Mr. Woolner made an exact model of one such case, and sent me the accompanying drawing.... The helix obviously consists of the extreme margin of the ear folded inwards; and the folding appears to be in some manner connected with the whole external ear being permanently pressed backwards. In many monkeys, which do not stand high in the order, as baboons and some species of macacus, the upper portion of the ear is slightly pointed, and the margin is not at all folded inwards; but if the margin were to be thus folded, a slight point would necessarily project towards the centre.... The following wood-cut is an accurate copy of a photograph of the foetus of an orang (kindly sent me by Dr. Nitsche), in which it may be seen how different the pointed outline of the ear is at this period from its adult condition, when it bears a close general resemblance to that of man [including even the occasional appearance of the projecting point shown in the preceding woodcut]. It is evident that the folding over of the tip of such an ear, unless it changed greatly during its further development, would give rise to a point projecting inwards[8].